1. Field of the Invention
The present invention relates to a touch-signal probe adapted to be used in a coordinate measuring machine, a machine tool and the like for measuring a configuration of a workpiece. More specifically, it relates to a vibrating touch-signal probe having improved sensitivity.
2. Description of Related Art
Conventionally, a height-gauge (linear measuring machine), a coordinate measuring machine, a contour measuring machine and the like are known as a measuring machine for measuring a configuration and a dimension of a workpiece. A touch-signal probe which detects a contact to a workpiece is employed in respective machines for detecting a coordinate and a position of the workpiece.
One simple way for detecting the touch of the touch-signal probe is to provide a contact portion for touching the workpiece at a tip end of an approximately cylindrical stylus to detect an opposing force caused by the touch. On the other hand, a vibrating touch-signal probe is also used, where a vibrating/detecting element is provided to the stylus to vibrate the stylus in advance and to detect a change of the vibration according to the touch. In the vibrating touch-signal probe, the vibration is changed, restrained for example, by the workpiece when the contact portion touches the workpiece. Accordingly, the contact can be detected by monitoring the vibration of the stylus to detect the change of the vibration.
The stylus of the vibrating touch-signal probe is preferably arranged radially. Especially, the stylus is most preferably arranged crosswise.
FIG. 4 shows a conventional vibrating touch-signal probe having styluses arranged crosswise. The touch-signal probe has a pair of stylus support 3 combined in X and Y-axis direction having a stylus 2 protruded thereon, a piezoelectric element 4 provided on an upper side of the respective stylus support 3 and a probe body 5 as a probe axis having the respective stylus supports 3 attached at a tip end thereof. A contact ball 2a provided at a tip end of the respective styluses 2 is abutted to the workpiece while the styluses 2 are vibrated by the piezoelectric element 4 to detect vibration change.
However, the contact ball 2a at the tip end of the stylus 2 is provided at a different height and can not be arranged at an identical level, since the stylus 2 is combined crosswise by stacking a pair of stylus 2. Accordingly, the vibrating touch-signal probe is difficult to use and is difficult to reduce size thereof.
In view of above disadvantage, a vibrating touch-signal probe having a contact ball at the tip end of the stylus arranged coplanar has been strongly desired. In response, the applicant has proposed a structure in which the stylus support of the touch-signal probe is vibrated on an identical level in a radial direction (Japanese Patent Application No. Hei 8-336986).
FIGS. 5(a), (b) and FIG. 6(a) shows a specific structure of the touch-signal probe proposed by the applicant.
A center of the stylus support 10 corresponds to the origin of X, Y and Z-axis. The stylus support 10 has a square X-Y plane and is a flat block. A pair of vibrating/detecting element 12 composed of a piezoelectric element is bonded to a locating projection 11 protruded on four corners of an upper and a lower surface of the stylus support 10. A total of four styluses 13 are provided on a center of respective sides of the stylussupport, the styluses being symmetrical and corresponding to X and Y-axis directions respectively.
The stylus support 10 is supported by fitting a tip end 15a of a probe body 15 extending in Z-axis direction to a fitting hole 14 penetrating through the plane center of the stylus support 10.
An insert hole 16 having sufficiently larger inner diameter than an outer diameter of the tip end 15a is formed at a center of respective vibrating/detecting element 12 to prevent the vibrating/detecting element 12 from being interfering with the probe body 15.
According to the above arrangement, a cross-shaped touch sensor having the ball-shaped contact portion 13a at the tip end of the respective styluses 13 disposed coplanar can be obtained, of which mechanism is simple and is adapted to size reduction.
However, according to the touch-signal probe structure shown in FIGS. 5(a), (b) and FIG. 6(a), the stylus support 10 deforms to be stretched and contracted in a radial direction (diametral direction relative to a central axis line of the probe body 15) as shown in FIGS. 6(b) and 6(c) when the vibrating/detecting element 12 is vibrated.
Accordingly, when the stylus support 10 is attached by fitting the probe body 15 to the fitting hole 14, the deformation of the stylus support 10 is hindered by the fitted probe body 15 and sufficient vibration can not be maintained. In other words, though the stylus support 10 has to be sufficiently vibrated for sharply sensing the contact to the workpiece, the stylus support 10 can not be vibrated for being fitted to the probe body 15 as mentioned above. Therefore, sensing accuracy can be deteriorated.